Recently, various kinds of a color liquid crystal display device (liquid crystal color display) have been developed and have been on sale. In order to improve the display quality of a liquid crystal panel, the liquid crystal display device is provided with a γ correction device for performing y correction with respect to an image signal to be inputted. Further, it is required to provide a correction characteristic determining device which can appropriately determine a correction characteristic of the γ correction.
Conventionally, as to a technique concerning the γ correction of the liquid crystal display device, Japanese Unexamined Patent Publication No. 127620/1993 (Tokukaihei 5-127620)(Publication date: May 25, 1993) discloses the following technique. In a projection-type liquid crystal display device, brightness and chromaticity of an actually projected image are measured, and the γ correction is performed while adjusting white balance to target chromaticity.
However, in the technique disclosed in Tokukaihei 5-127620, a target mixture ratio of RGB is calculated, in accordance with (a) the target chromaticity that has been set in advance and (b) actually measured chromaticity, while adjusting the white balance, but characteristics of respective display devices are not taken into consideration upon calculating the mixture ratio of RGB. More concretely, in the technique disclosed in the foregoing publication, the target mixture ratio of RGB is calculated by using chromaticity obtained in a case where each color of RGB is projected as a single color, but chromaticity obtained in a case of white display is not taken into consideration, so that the target mixture ratio of RGB is calculated without considering brightness difference etc. among RGB in an actual display device.
Thus, in the technique disclosed in the foregoing publication, even though display is subjected to the correction, the actual mixture ratio of RGB deviates from the target mixture ratio of RGB due to difference in the characteristics of the respective display devices.
Further, in the technique disclosed in the foregoing publication, a characteristic of a black state at a low gray scale area of the liquid crystal display is not taken into consideration, so that a target curve (curved line indicative of a target value of output brightness with respect to a gray scale value) sometimes indicates indisplayable brightness (a value at which the display cannot be performed in the liquid crystal element) as shown in FIG. 10(a).
For example, even when a target value indicated by the target curved is 0 at the lowest gray scale area, a bit of brightness and a bit of chromaticity are sometimes obtained in a case where the lowest gray scale is actually displayed in the liquid crystal element so that the brightness and chromaticity thereof are measured. Thus, the target value “0” is a indisplayable value at which display cannot be performed in the liquid crystal element, and it is necessary to adjust the target value at the low gray scale area so as to set the target value to be displayable.
Further, upon adjusting the target value at the low gray scale area, in a case where the target value at the low gray scale area that has been adjusted as shown in FIG. 10(b) does not smoothly shift to a target value of a middle-high gray scale that has not been adjusted (a case shown in FIG. 10(c)), the brightness and chromaticity greatly vary in the vicinity of the foregoing gray scale in the display device having been subjected to the adjustment, so that this sometimes causes a low quality image.